Preparation and characterization of self-assembled alkanephosphate monolayers on glass substrate coated with nano-TiO₂ thin film

Self-assembled alkanephosphate monolayers on glass substrate coated with sol-gel TiO₂ thin film were prepared by means of molecular self-assembly process. The wetting behavior and structure of the alkanephosphate monolayers were characterized by means of contact angle measurement and X-ray photoelectron spectroscopic analysis. The friction behavior of the glass substrate coated with TiO₂ thin film and the alkanephosphate SAMs in sliding against an Si₃N₄ ball was examined on a one-way reciprocating friction tester. As a result, water contact angle on alkanephosphate SAMs is at 90-104°. The SAMs of alkanephosphate are bonded to the TiO₂ covering layer on the glass substrate by way of monodentate and bidentate coordination. In n-monoalkanephosphate SAMs, the monodentate and bidentate of adjacent phosphate headgroups are linked by intermolecular hydrogen bonding. The SAMs of long chain n-monoalkanephosphate show considerably decreased friction coefficient in sliding against the Si₃N₄ ball under low load, compared with the TiO₂ covering layer on the glass substrate.